(1) Field of the Invention
The present invention relates to microelectronics and particularly to improving the high frequency performance of integrated circuits which, in part, have very fast switching times. More specifically, this invention is directed to methods of and apparatus for decoupling switching transients and other high frequency noise from the power supplies for integrated circuits. Accordingly, the general objects of the present invention are to provide novel and improved methods and articles of such character.
(2) Description of the Prior Art
It is well known in the field of microelectronics that high frequency operation, particularly the switching of integrated circuits, can result in switching transients being coupled into the power supply circuit. There have, in the past, been several techniques proposed for preventing the coupling of undesired high frequency interference into the power supply circuit for an integrated circuit wherein the noise is generated. Thus, for example, it is known to employ low pass filters which are connected between the common power supply leads of an integrated circuit. Such low pass filters include decoupling capacitors which are mounted on a printed circuit board and connected by traces on the board to the plated through-holes which receive the ground and power supply connection leads of the integrated circuit. This technique has several deficiencies. The most serious of these deficiencies resides in the fact that the circuits including the capacitors become highly inductive at high frequencies as a consequence of the shape and length of the leads and interconnection traces between the discrete capacitor and the integrated circuit which it decouples. The inductance of the leads and printed circuit board traces may be sufficiently high to nullify the effect of the capacitor in the circuit. A second serious deficiency resides in the inherent volumetric inefficiency incident to employing a low pass filter which requires a discrete capacitor. The space requirements of the capacitor and the interconnection traces on the printed circuit board adversely affect the component packaging density which can be achieved.
In an effort to overcome the above-discussed deficiencies associated with the use of low-pass filters with discrete decoupling capacitors mounted on a printed circuit board, it has been proposed to provide sockets which receive the integrated circuit and which have a decoupling capacitor formed integrally therewith. An example of this approach may be seen from U.S. Pat. No. 3,880,493. While an improvement over the previous technique of employing low-pass filters, the technique of U.S. Pat. No. 3,880,493 also has certain inherent deficiencies. Firstly, the socket with integral capacitor is a comparatively complex and thus expensive component. Secondly, the patented technique is also characterized by volumetric inefficiency since, in effect, it comprises a socket mounted above a socket which is mounted above a printed circuit board; the uppermost socket being that in which the integrated circuit is packaged.